Remote-control device



July 20,

Filed Jan.

, 1954 c. K. AuvlL 2,684,472

REMOTECONTROL DEVICE l0, 1949 4 Sheets-Sheet l a 27 25 21 g za 2217 #Q -*h 22 "22a zal 26 7 i c f "I7 21. u l', 25 27K /l 57 /l 21 56 @a 88 T frs 24 22 25 f/f "Lf-UW \23 5+ 11m/W5 [/ZZb C. K. AUvlL REMOTE-C0NTROL DEVICE July zo, 1954 4 sheets-sheet 2 Filed Jan. l0, 1949 CnmeaL L K. A uv/L,

RTTORNEYS.

July 20, 1954 c. K. AuvlL REMOTECONTROL' DEVICE 4 Sheets-Sheet 3 Filed Jan. 10, 1949 INVENTOR 'CnRRoLL K. Huvu.J

ATTORNEYS.

July 20, 1954 Q K AUVIL 2,684,472

REMOTECONTROL DEVICE Filed Jan. l0, 1949 4 Sheets-Sheet 4 B+ Wj Patented July 20, 1954 UNITED STATES itATllNT attain OFFICE 3 Claims. l

This invention relates broadly to an improved means and method for communicating intelligence by the use of electrical signals having a frequency or" the order of audio-frequency signals. Various systems have heretofore been proposed in which variations in the frequency of such a signal have been employed for purposes of eiiecting a remote control, for telemetering, and for the communication of intelligence in general. Prior systems of this kind of which I am aware have been open to several objections among which may be noted their employment of heavyI and complicated apparatus and relatively broad frequency bands. In many situations, as in the remote control of model airplanes or guided missiles for example, excessive Weight is a disadvantage. In the same or in other situations, wide frequency bands may objectionably limit the number of audio-frequency signals which can be transmitted by a single carrier.

It is therefore an object of this invention to provide a simple apparatus employing variations in the frequency of an electric signal for telee metering, for remote control, or for otherwise communicating intelligence. Another object of the invention is to produce an apparatus which Will be highly sensitive to small variations in frequency, which may therefore possess a Wide range of operation under the control of frequencies ly-y ing within a narrow band, and which will not be objectionably sensitive to variations in the amplitude or to harmonic distortion of the tran mitted signal. A further object is to produce an improved current-controlling device which Will respond` promptly and with a high degree of sensitivity to variations in the frequency oi a controlling signal. Another object oi my invention is to provide an improved currentresponsive device for effecting mechanical movements. Still another object of the invention is to provide a system which will not be adversely aiiected by harmonic distortions or amplitude variations in the controlling signal.

My invention involves the expedient of conn trolling the current in an electron discharge device jointly by two cyclical electrical signals have ing a frequency of the order of audiodrequency signals. One of such signals is a control signal to variations in the frequency of which the ap paratus is to be responsive. Conveniently, the two signals are impressed respectively on the control and screen grids of a tetrode or pentode, so that the potential of each grid can limit plate current to a minimum irrespective of the pon tential on the other grid. As a result, the elecso i,

tron discharge device will pass plate current only during intervals When both grids are above their respective cut-off potentials. If the two signals are of the saine frequency, their successive Waves will possess a uniform phase relation, and the duration of each interval in which plate current ows will be constant. However, 4if the control signal undergoes a slight change in frequency, a progressive Wave-to-Wave change in phase relation will occur, the duration of the currentpassing intervals Will change progressively, and the average plate current will either increase or cli-- minish. Means responsive to the change in plate current is provided for causing the frequency oi the second signal to be brought into agreement with the new frequency of the control signal. The same current-responsive means or another may be employed to indicate the changed frequency or to perform other functions. To prevent amplitude-variation or distortion of the transmitted signal from adversely affecting response, the transmitted signal is not itself used as the control signal; but instead the control signal is the output oi a local oscillator capable of following changes in the frequency of the transmitted signal.

The accompanying drawings illustrate my invention:

Fig. 1 is a diagrammatic view illustrating the receiving station of a system especially adapted for telemetering; Figs. 2, 3, and 4 are curve diagrams drawn to the saine time scale illustrating the eect of changes in signal frequency; Figs. 5 and 6 are diagrammatic illustrations respectively shoiving the transmitting station and the receiving station of a remote-control system; Figs. 7 and 8 are respectively a plan and an elevation illustrating one mechanism by which rcechanical movement may be reproduced at the receiving station shown in Fig. 5; Figs. 9 and 9a are diagrammatic views illustrating modified forms of remote-control receiver; Fig. 10 is a diagrammatic view illustrating still another remote-control receiver; Fig. 10c is a view similar to Fig. 8 showing mechanical mechanism suitable for use in conjunction with the system of Fig. l0; Figs. il and 12 are curve diagrams illustrating the operation of the system shown in Fig. l0; and Figs. 13 to i6 are curve diagrams eX- planatory or" some general aspects of my invention.

The apparatus illustrated in Fig. l is a receiver particularly suited for telemetric purposes. lt comprises a milliammeter 2li, which constitutes the remotely controlled telemetric indicator, connected in parallel with a resistance 2l in the plate circuit of an electron discharge device 22. Desirably, a resistance 2t' is connected in series with the milliammeter 26. The electron discharge device embodies a pair` grids 22a and 22h, which conveniently, but not necessarily, are the nominal control grid and nominal screen grid of a single tetrode or pentode, but both of which function as control grids in the apparatus illustrated. The grid 22a is connected to a conductor 23 transmitting a cyclical signal We the frequency of which varies v/ith the variable Whose value is to be indicated by the miiliainnieter 2o. The grid 22h of the tube 22 is connected toa conductor 2t which transmits a cyclical signal Ws locally generated, as by an oscillator and impressed on the conductor 2d through anisolator 25. The oscillator 25 is of a type such that *he frequency of the signal it creates will vary with a voltage impressed upon it. lt is vned herein that the frequency of the signal generated by the oscillator 25 varies the same sense as does the controlling voltage, but that is not essential. In the apparatus shown in Fig. i, the controlling voltage is that existing at a point 2 ic along the resistance 3i. A condenser 2'? connected in par allel with the resistance il and the milliammeter 2i! may be employed to smooth out nuctuations in the plate current of the tube 22. Apparatus suitable for generating the audio-frequency signalsy Wc and Ws will be described in det il hereinafter. The signals We and Ws are indicated in Figs. l to 4 as of sineWave and square-Wave form respectively; but While this is desirable in some instances, it is not at all essential in the practice of my invention.

Figs. 2, 3, and 4 are horizontally co-ordinated views illustrating the effectsof changes in the frequency of the signal We. In all three figures, it is assumed that the cut-oil potential of both grids 22a and 22h coincides with the horizontal axis of the curve We.

Fig. 2 illustrates a stable-state condition eX- isting When the frequency of the signal Vic is constant and equal to the frequency'of the lon cally generated signal WS. The area of each of the shaded regions of Fig. 2 constitutes a measure of the quantity of electricity flowing in the plate circuit of the tube 22 at each cycle; and the aggregate area of the shaded regions for unit time is a measure of the average plate'current. he signal We is shown as leading the WS; and, as a result, if the frequency of We decreases slightly a progressive Wave-totvave decrease in phase displacement of the two signals Will oc" cur to cause an increase in the current flowing in the plate circuit of the tube 22. rlhis condition is illustrated in Fig. 3, from Which it will be evin dent that the shaded regions progressively increases in area from wave to Wave or" the signalV We. As current in the plate circuit increases, the potential at the point 2id decreases to decrease the frequency of the signal WS; and eventually a new condition of equilibrium is attained at which the frequencies of We and We Will again equal each other. This condition is illustrated in Fig.V Ll, which shows that the two signals, although novv of the same frequency', have a different phase relationship from that illustrated in Fig. 2. This change of phase relationship results in an increase in the area of the shaded regions corresponding toan increase in plate-circuit current just sufficient to drop the potential at the point .2 la to a value which will result in coincidence between the frequencies of We and Ws.

In similar manner, if the frequency of the con trol signal We is increased, the lead of its successive waves will increase, plate-current will decrease, and the potential at point 25a Will increase until the frequency of We matches that of W5 to establish a new stable-state condition.

From the above, it will be obvious that the plate current of the tube 22 is a function of the frequency of signal We. lt will also be obvious that as the current flowing in the milliamrneter 2G bears a constant ratio to total plate current, the reading of the milliammeter will likewise be a function of the frequency of We. If the frequency of We is caused to vary with some variable quantity, the reading of the inilliarnmeter 2li becomes a measure of the variable.

The function of the resistance 2t is to decrease the fraction of plate current which flows through the r niammeter and hence to increase the magnitude of the frequencycontrolling potential variations which occur at the point Ela. The magnitude of potential Variations at the point Zia will also be aiiected by the location of that point along the resistance 2i; and in consequence it is possible, by shifting the point 21a,- to vary the eiect of a change in the frequency. of the signal We upon the reading of the milliammeter. The condenser 2l should possess a capacity large enough to prevent current through the resistance 2i from dropping to zero in the interval between successive periods in which Wc and Ws are both positive; but if its capacity is large enough to prevent the voltage at the point, 2 la from rising with adequate speed upon adecrease in plate current caused oy an increase in the frequency of the control signal, supplementary equipment Will be required if the system is to respond properly to a maximum increase in the frequency of the control signal.

Figs. 5 to 8 illustrate a remote-control system operating on the same general principle as that employed in the apparatus of Fig. 1. The remote-- control system embodies a transmitting station (Fig. 5), from which control is to be exercised, and a receiving station (Fig. S) at which are located the elements to be controlled. For each of the controlled elements there is an electron discharge device, shown in Fig. 6 as a pentode 22', corresponding in function to the tetrode 22 of Fig. l. Each pentode 22' has grids 22a and 22h, the respective potentials of which jointly control plate current, and mechanism responsive to changes in plate current is provided for moving the associated controlled element.

The apparatus at the transmitting station, illustrated in Fig. 5, comprises a radio transmitter Eil the output of which is modulated by the signalv or signals produced by one or more control units lator i3 the output or" which is supplied through isolation tube 35 to the radio transmitter 3Q. The oscillator 32 is conveniently of the resistancecapacity, phase-shift type and includes in its plate circuit a frequency-controlling potentiometer adjusted by a movable control member S5 the movements of which areto be reproducedor followed by a controlled member at the receiving station. In addition to the potentiometer 3s,

plate circuit ofy the oscillator 32 desirably includes a small variable resistor Se employed for trimming purposes.

At the receiving station, illustrated in Fig. 6, l provide a movable controlled member El for each of the control units 3l at the transmitting station. The apparatus herein described func- Each oi such control units comprises an oscil-V tions to cause the controlled member 40 to reproduce or follow the movements of the correspending control member at the transmitting station. Movement of the controlled member lo is eiected through the medium of electromagnetic device, indicated in Fig. 6 as a pair of electromagnets Ill and 42, connected in the plate circuit of the pentode 22. One specific form of means for moving the controlled member 40 is set forth hereinafter; but in its broader aspects, my invention comprehends any mechanism capable of moving the controlled member il in one direction upon an increase in the plate current of Irhe pentode 22 and in the opposite direction upon a decrease in such current.

The pentode 22 corresponds in function to the tetrode 22 of Fig. 1, its plate current being controlled jointly by the respective potentials of the grids 22o and 22h. As in Fig. l, the grid 22h has impressed upon it a signal (WS) generated by a local oscillator 25. Desirably, the control signal (We), which is impressed on the other grid 22a, is the output of a second local oscillator 46 capable of departing to a limited extent from its nominal, freely oscillating, frequency under the iniuence of exteriorly generated frequency imposed upon it. Conveniently, the oscillator l5 is of the resistance-capacity, phase-shift type in which a portion of the output of a tube 53 is fed back to the grid of such tube through a series or" condensers. rlhe parameters of the oscillator 4t are such that its nominal, or freely operating frequency, is approximately equal to one midway between the minimum and maximum frequencies generated by the corresponding control unit 3i at the transmitting station. The receiving station embodies a radio receiver il which is tuned to the frequency of the transmitter lill and the signalfrequency output of vhich is impressed. desirably through a blocking condenser 48 and an isolating resistor til upon each of the oscillators it at the receiving station. The output of the oscillator iii is impressed, desirably through a resistor 5l, upon the control grid 22d.

As previously indicated, the oscillator 4B is capablo of departing to a limited extent from its nominal frequency under the influence of a slightly diierent frequency impressed upon the control grid of the electron tube 53 forming part of such oscillator. The tendency of the oscillator 46 to loch in with an impressed frequency may be increased by reducing the elective ligure of merit of the oscillator' circuit, which result can be accomplished in an oscillator of the type shown by the use of a resistor 5d connected as indicated in Fig. t?. It will be understood that the receiving station embodies one oscillator it for each of the control units 3l at the transmitting station and that the nominal frequencies of the several oscillators lli will respectively approximate the mean frequencies generated by the control units 3l. As a potentiometer 3d at the transmitting station is adjusted to vary the frequency of the signal generated` by the control unit, the transmitted signal, impressed at the receiving station through the condenser i8 and resistor 49 on the corresponding oscillator llt, will cause corresponding variations in the frequency of the output of such oscillator. Variation in the output aniplitude of the oscillator lli due to variations in the frequency of the incoming signal can be reduced by connecting the resistance 49 to the grid of the tube 53 through one of the condensers in the feed-back circuit rather than directly. To reduce interference between the several oscillators 46 at the receiving station, the resistor 49 should possess a resistance equal to several times the output impedance of the receiver 4l. Preferably, the resistance of the resistor 49 should be at least ten times the output impedance of the receiver.

The oscillator 25 is conveniently a multivibrator, shown as embodying a triode 56 and a pentode t?, condensers 58 and 59, and resistors 5t and 6|. is well known, the characteristics of the output of a multivibrator such as is shown in Fig. 6 can be varied varying the capacities of the condensers 5:? 5S and the resistances of the resistors and 5l. Desirably, these parameters are selected so that the output of the oscillator 25 will have the approximate symmetrical wave form indicated at W5 in Figs. 2 to 4. The nominal frequency of the oscillator 25 is substantially the same as the nominal frequency of the associated oscillator at, but is subject to variation under the control of a potentiometer t5 responsive to movements or" the controlled member l and connected in series with one of the resistors @El and 6l. An adjustable resistor Eli, serving as a trimming resistance, is conveniently provided in series with the potentiometer t5. As previously indicated, the output of the oscillator 25 is impressed, desirably through a cathode follower isolation tube 25. upon the grid 22?), or" the pentode 22.

It will be obvious that in the apparatus of Fig. G the current nov/ing through the electromagnets di and d2 will be under tie ljoint control or the voltages respectively impressed upon the grids 22a. and 2b of the pentode 22'. In somewhat the same manner as is illustrated in Figs. 2 to 4 and above described, a change in the frequency in the signal impressed on the grid 22a will cause a change in the current flowing through the electromagnets 4! and 42. By mechanism hereinafter described, the change in the current ilowing through the magnets di and 42 will cause movement of the controlled member 4Q, and the movement of the controlled member Will in turn adjust the potentiometer fic to bring the frequency of the oscillator 25 into agreement with that of the signal impressed on the grid 22a.

While the operation of the system shown in igs. 5 and 5 resembles that shown inFig. l in that differences in frequencies between a control signal and a local signal respectively impressed on two control grids of an electron discharge device cause the frequency of the local signal to match that of the controlling signal, there are some diierences in mode or" functioning between the two systems. As brought out in Figs. 2 to 4, a different plate current and a different phase relationship or" the two signals We and We exist in the apparatus of Fig. l for each stable-state condition in which the frequencies of the two signals are matched. In the system of Figs. 5 and 6, however, substantially the same plate current exists for all stable ,tate conditions; since any departure or" the plate current from its normal value would cause the electromagnets il! and di! to operate, move t. -e movable controlled member di?, and e potentiometer S5 to alter the frequency of the o ator Z5. Some change in phase relation-hip or the signals will occur in the system s. 5 and 6 since the average plate current, which controls the magnets di and e2, is a function or both the frequency and the quantity or" electri ity flowing per cycle in the plate circuit. In order for average plate current to remain the same in different stable-state conditions, the lead of We over Ws will be less at Vtorque is applied.

Vcornprises a rotatably supported shaft 15 to which Va substantially constant, uni-directional When the system is employed for controlling gasoline-powered model airplanes, the torque applied to the shaft l5 may be derivedfrom a twisted rubber band l5. Loosely mounted on the shaft 'i5 are a pair of frames Ts and TS which respectively support the electromagnets -t-l and (il. Such magnets have respectively associated with them bra-lie mechanisms it and Bil cri-operate with a disk Si rotatable with the shaft The arrangement is such that when either is engaged its associated frame 'Il or l is clamped to the disl 8i and tends to rotate therewith. The brake mechanism is is controlled jointly by the electromagnet 4i and a second electromagnet S2 supplied with a constant current. A xed magnet uld be substituted for the electromagnet d2 if desired. The arrangement is such that the two magnets fil and S2 exert opposite effects on the brake mechanism le, with the effect of the magnet S2 predominating over that of the magnet il to hold the brake is engaged whenever the current in the magnet el is at or below its normal value. The magnet l2 acts to hold the brake 3" in engagement whenever the current in it is at or above the normal value. The frame l'l' and S, include por ions of non-magnetic material such as may be necessary to isolate the magnetic circuits, are individually connected by linlrs ll and i3 to the controlled member @il which is in turn connected in any appropriate manner to the movable element of potentiometer se.

When normal plate current flows through the electi'ornagnets il and i2 both brake mechanisms 'le and Se will be engaged to lock the frames 'il' and 13 to the disk Si. In this condition, the disk. and frames cannot rotate, since the two frames are connected by the links Ta" and 'i8' to the longitudinally slidable operating member et. Should plate current increase from the normal value which both brake mechanisms le and St engaged, the electromagnet l would overcome the brake-engaging effect of the magnet t2 to release the brake meohanisnl 'l thus freeing the connection between the disk Si and the frame 'il and permitting the disl; 3i to rotate. The eiect increased current in the magnet l2 merely tightens the grip of the brake 3D in the disk 3i, and as the disk rotates it therefore carries the frame is with it and moves the controlled member o upwardly. Such movement of the controlled member, transmitted to the frame Vi through its associated link il', causes the frame ll to swing in a direction opposite to that in which the disk el rotates. in addition, upward movement of the controlled member et adjusts Vthe potentiometer 55 to decrease the frequency of the oscillat 25 and cause the plate current to decrease, in the manner above described, until the magnet el is incapable of overcoming the effect of the magnet 32, whereupon the brake I engages the disk s! and prevents any further rotation thereof.

Should the plate current decrease from the value necessary to maintain both brakes i9 and 80 engaged, such decrease would be without any signicant eifect on the brake i9, which is held engaged by the magnet 82, but would partially cle-energize the electromagnet l2 and release the brake si). The disk 8i is thereby freed for rotation; and in its rotation it carries the frame il with it to more the controlled member t9 downwardly causing an adjustment of the potentiometer @5 which, by increasing the frequency of the oscillator 25, eventually causes the plate current to increase until the brake 8e is again engaged.

It is to be understood that the mechanism illustrated in Figs. 7 and 8 is shown and described merely by way of example and that my invention is not limited to any specific mechanism for converting changes in plate current into movement of a controlled member and rez-adjustment of the local oscillator 25.

To take account of delay in operation of the mechanism controlled by theV electromagnets fil and 132 a resistance et may be connected between the B+ source and the potentiometer and a condenser may be connected. between the plate of tube 22 and the low-potential terminal 58 of the resistance 558. With such an arrangement, the resistance 68 functions in somewhat the same manner as does the resistance .2l in Fig, l; that is, it causes a change in plate current to create a change in the potential to which the condenser 59 attempts to charge, and by so doing it changes the frequency of the oscillator Accordingly, upon a change in plate current caused by a change in the frequency of the control signal, the frequency of the oscillator 25 will be changed substantially immediately to match the new frequency of the control signal, whether or not the mechanical system responds with sufficient speed to effect that result. in other words, except where the change in frequency of the control signal proceeds with such extreme slowness that the mechanical system alone accounts for the matching change in the frequency of the oscillator 25, the changed frequency of such oscillator will be due at least in part to an abnormal potential at the point 66', which abnormal potential will in turn be due to abnormal plate current. However, any such condition is transient in character, both because the abnormal plate current causes further adjustment of the potentiometer 535 and because the condenser Se, as a result of its edect on the potential at point t8 and the effect of that potential in the frequency of the oscillator tends to maintain an abnormal plate current until the potential at the point -55 returns to its normal value and the new frequency of the oscillator is clue entirely to adjustment of the potentiometer 65. As a result, even though the frequency of the oscillator 25 may be'brought into agreement with the changed. frequency of the control signal more rapidly than can be caused by movement of the controlled member and readjustinent of the potentiometer, movement of the controlled member te and readjustment of the potentiometer 55 continues until the changed frequency of the oscillator is entirely accounted for by potentiometer-readjustment. When this stage is reached, the plate current will have again attained its normal value and the controlled member lo will occupy the position determined for it by adjustment of the corresponding control member 35 at the transmitting station.

In Fig. 9 I have illustrated a remote-control receiving system which differs somewhat from that illustrated in Figs. to 8. In this system, the clement to be remotely controlled is the rotor 84 of a servo-motor 85 having two field windings 86 and 8S arranged to oppose each other in their effect on the rotor The neld winding 3S is energized by a suitable current source il under the control of a potentiometer t3 which is operatively connected in any convenient manner, as indicated diagrammatically by dotted lines in Fig. 9, to the rotor 815. The field winding is shown as replacing the milliammeter 2c and resistance 2li in the system of Fig. 1.

In the device just described, the position of the rotor es will be a function of the current nowing in the eld winding for upon any change in such current. the rotor will rotate and adjust the potentiometer 88 until the curre. t in the winding 36 just counterbalances thatl in the winding whereby to bring the rotor to rest. As was brought out in the discussion of Fig. 1, the stable-state plate current in the tube f2 will have a different value for each frequency of the control signal. Since current in the winding et will be proportional to such plate current, the rotor 84 Will have a different position for each frequency of the control signal, and by varying the frequency of the control signal the position of the rotor 84 can be controlled as desired.

Reverting to Figs. 2, 3, and a, it will be apparent that maximum plate current will new when the two signals We and Ws are in phase with each other or nearly so and that minimum plate current will flow when the two signals are displaced in phase by 180 or thereabouts. In the systems of Figs. 1 and 9, the frequencies corresponding respectively to maximum and minimum plate currents determine the limits of the frequency band Within which the frequency of the control signal We may vary while the system remains operative.

Another condition limiting the width of such frequency band is indicated in Fig. 13. Since the joint controlling effect of the two signals We and W5 is exerted only during intervals in which both of them are positive, any phase displacement occurring when one or both signals are negative is without any immediate effect on plate current. It is conceivable that in the interval between successive periods in which both signals are positive, the signal Wc could undergo a change in frequency sufficient to reverse the normal controlling effect. Fig. 13 illustrates a stable-state condition terminating at time A. During the existence of the stable-state condition, the signal We has a slight lead over the signal Ws. At the point A, which marks the termination of a period in which both signals are positive, it is assumed that the signal We undergoes a decrease in frequency sufficient to reverse its phase displacement relative to the signal WS and to increase the absolute Value of such displacement at the next period in which both signals are positive. In such a case, the immediate effect of the changed frequency of the control signal would be to decrease plate current, as is indicated by the fact that the third shaded area in Fig. 13 is smaller than either the rst or second. This decrease in plate current, occurring in any of the systems described, would, either directly or indirectly, tend to increase the frequency of the signal Ws. That is, the frequency of signal Ws, instead of changing in the same sense as that of signal Wc, would change in the opposite sense and the system, if operative at all, would be highly erratic.

To avoid the occurrence of any such a condition the band of frequencies over which the control signal WC is variable may be restricted to such an extent that the signal We can never, Within one cycle, shift from a leading to a lagging phase relationship with respect to the signal Ws. With symmetrical signals, anc depending to some extent on wave-form, such a result is substantially attainable by limiting to one-fourth the mean frequency the extent to which the frequency of the signal We can depart in either direction from such mean frequency. If at the nominal frequ ncy the signal We leads the signal Ws by 90, am. if the i oquency of We can not depart by more than one-fourth from its nominal value, no decrease in the frequency of We, no matter how abrupt, can cause it to change from a leading to a lagging phase relationship within one cycle.

When both of the signals We and WS are syml, they have been assumed to be above, plate-current can be changed from its maximum to its um value, or vice Versa, by a change f i the phase relationship of the two signals. s just brought out, the range of change in phase relationship of the two signals can be restricted to 180 by limiting to one-fourth of the nominal frequency the extent to which the frequency of the control signal can depart, in either sense, from such nominal frequency. In other words, if the signals are symmetrical, and if it is desired to utilize the full range of platecurrent variation, the band width throughout which the frequency of the control signal is variable should be substantially one-half the mean frequency of that signal. In Fig. le, I have illustrated asymmetric signals We and Ws of square wave-form comprising positive pulses each of approx "nately 90 in extent. It will be obvious from that ligure that the full range of plate-current variation can be attained within a 90 change of phase displacement. That is, if the two signais are in phase, maximum plate current will be passed; but if the two signals depart from in-phase relationship by el? there will be no periods during which both signals are positive, and therefore plate current will be at a minimum. As the change in control-signal frequency necessary to produce a 90 shift in phase displacement is obviously less than that required to produce a 186 shift, it follows that asymmetric signals permit the band-width of the control signal to be reduced without reducing the range of platecurrent variation.

Fig. 15 illustrates a combination of wave forms in which the phase displacement may be greater than lSD. As there shown, the signal We has a saw-tooth form, while the signal Ws has an asymmetric square wave form. lll/ith such Wave forms, the phase displacement may vary through an angle equal to the difference between 860 and the angular measure of the duration of the positive pulses of WS; and the band-width allocated to the signal We must be accordingly enlarged if the full range of plate-current variation is to be obtainable.

It can be demonstrated that the rapidity with which a receiving system adjusts itself to a given change in the frequency of the control signal is a function of the band-width necessary to obtain immediately the full range of plate-current variation. Specifically, the narrower such band width, the more rapidly will the receiving system respond. It follows from the above discussion of Fig. le that by decreasing the proportionate duration of the positive pulses of asymmetric signals the band width can be reduced Without reducing the rate at which the system responds to a given change in control-signal frequency. Ii the signals are of square Wave form, the total band Width bears the same ratio to the mean frequen-cy as the duration of each positive pulse bears to the period of a full cycle. While the rapidity with which the receiving system adjusts itselr" to a given change in signal frequency can be preserved While reducing the band-Width, the increase in the asymmetric character of the signais which is necessary to permit the reduction in band-Width causes a reduction in the duration of the periods in which both signals are pos'- itive and a consequent reduction in average plate-current. The reduction in plate current can be prevented to some extent by increasing the amplitude of the signals; but there are practical limitations upon the benefits obtainable by increasing signal-amplitude.

ln Fig. li? l have indicated an expedient by which the reduction in plate current which, as just set forth, normally accompanies a reduction in band Width, can in some measure be avoided Without the necessity for an undue increase in amplitude. ln the practice or" that expedient, plate current controlled not directly by the joint elle-ct ci the tivo signals We and vifs, but instead is controlled'jointly by two auxiliary signals VC and Vs. The signals Vc and ifs are oonveniently such as might be produced by multivibrators havi; g a frequency several times the normal frequency of the signals 'We and Ws and arranged to be triggered respectively by the latter signals. The output of such a multivibrator would consist oi groups of positive pulses, the duration and spacing of the pulses in each group being determined. by the characteristics of the in"ltivibrator and the frequency of the groups being determined by the frequency of the triggersignals. For simplicity of illustration, Fig. lo shows each signal Vc and Vs as comprising but two positive pulses per Group; but it will be understood that t le number of pulses per group may be increased to three or more.

in a system employing the expedient indicated in Fig. lo, the band Width of the signal We necessary to vary plate-current throughout its entire range will depend upon the duration of each positive pulse of the signals Vc and Vs; and as there are a plurality oi such pulses per cycle of the control signal, the duration of each will necessarily be relatively small. As a consequence, a narrow band Width for the signal We Will permit the full ange of variation in plate current. Because there are a plurality of the positive pulses of the signals 'ic and Vs per cycle of the signals We and WS, instead oi but one as in Fig. lll, the amplitude of the signals VC and VS can be reduced While still maintaining average plate current within the desired range.

ln both the systems so far described, stablestate conditions are characterized by the existence of plate current. In some situations, it may be desired that no plate current flow under any stable-state condition; and a receiving system possessing that advantage is illustrated in Fig. 10. That system embodies a multivibrator 2e generally similar to and embodying the same principal elements as the multivibrator previously described. As in Fig. 6, one of the frequency-controlling resista-noos et and el of the multivibrator is connected to the B-l.- source in series with the adjustable potentiometer E5 and the xed resistance 68, so that the frequency of the current generated by the mutlivibrator 2o may be adjusted by the potentiometer 6E. The

function of the multivibrator 25' is somewhat different from that ofV the multivibrator 25; and in order to enable it to carry out that function in the manner contemplated, its nominal frequency is twice that of the nominal frequency of the control signal.

The plate of the triode 5t of the multivibrator 25 and the screen grid of the pentode 5l are' each connected to ground through a condenser and resistance 9! arranged in series, as indicated in Fig. 1G. The ungrounded terminals oi the resistances El are connected respectively to opposite ends a resistor 92 and to the cathodes of rectifying diodes 93 Whose plates are grounded. The condensers et and their respectively associated resistances 9i serve to convert the substantially square Wave generated by the multivibrator into a series of alternating positive and negative peaks, the latter being passed to ground through the diodes t3 and the former being impressed in alternating relation on the opposite terminals of the resistance 92. fis a result, the potential at the midpoint of the resistor il? intermittently and brieiiy swings positive at a frequency twice that of the oscillator 2li.

The peaks of positive potential occurring at the midpoint of the resistance Q2 are employed to trigger and modify the frequency of a multivibrator es the nominal frequency of which is one-half that of the multivibrator 25 and therefore the same as the nominal frequency of the control signal. The multivibrator 95 comprises a trode El", a pentode condensers 5S and 5t', and resistances il and 5 l The mu tivibrator @il also includes resistances e6 in series with the grid of the triode 55 and the control grid of the pentode 5l. The peaks of positive potential occurring at the midpoint of the resistance s2 are imposed on the grids of the tubes t and 5l through isolator tubes Gl and the resistances As will be apparent to those skilled in the art, the effect of the peaks of positive potential imposed on the grids of the tubes 55 and 5l is to maintain the multivibrator 95 at a frequency equal to one-half the frequency of the multivibrator 25, when the latter frequency varies from its nominal value.

The substantially square-wave signals produced respectively by the oscillators 25 and Q5, the former signal having twice the frequency of he latter, are combined to product first and second asymmetric signals which are impressed respectively on the grids of the tWo triodes Il and lei. The apparatus employed to form the nrst asymmetric signal comprises a triode E62 arranged as an isolator and cathode follower and having its plate connected to the B-lsource and its cathode grounded through a resistance N33. The grid of the triode m2 is connected through a condenser ist to the screen grid of the pentode tl in the oscillator 95 and is also connected to the midpoint of a voltage divider la? connected between the B+ source and ground. The cathode of the triode i and the plate of the pentode el in the oscillator are connected through c identical condensers llil with the grid of triode lot, and the mean potential of the grid oi triode lli@ is maintained at cut-off as by a biasing battery lill'.

The net effect of the apparatus just described is indicated in curves C, D, and of Fig. ll, curve C representing the alternating potential of the plate or the pentode 5l, curve D indicating the alternating potential of the cathode of triode im,

and curve E representing the resultant asymmetric signal applied to the grid of triode |00. The horizontal axis of each of the curves C and D is at a potential equal to one-half the B+ potential, while the horizontal axis of curve E is at the cut-off potential of the grid of triode ilil as a result of the presence of the battery |61. When both condensers idc pass positive pulses, the potential of the grid of tube |69 rises above cut-Oil; when both condensers pass negative pulses, the potential of the grid drops below cutoi; and when one condenser passes a positive pulse and the other a negative pulse, the grid remains at cut-ori potential. As a result, plate current in the tube le@ is as represented by the curve F in Fig. 10, the frequency of the positive pulses being equal to the frequency of the oscillator Sii and their duration being equal to onefourth the period.

To produce the second asymmetric signal I employ a triode il@ which serves both as an isolator and to invert the alternating potential of the screen grid of the pentode l in the oscillator 25. The cathode of tube lill is grounded, while the anode is connected through a resistance to the B-lsource. rlhe potential applied to the grid is that existing across a resistance connected in series with a condenser H2 between the screen grid of triode al and ground. The plate of tube il@ and the plate of the pentode 5l in the oscillator 95 are connected through identical condensers H4 with the grid of the triode icl.

The eiect produced by the apparatus just described is indicated by the curves G, H, and I of Fig. 10. The curve G is the saine as the curve C except for its inversion, the curve H is the same as the curve D, and the curve l is both inverted and displaced in phase with respect to the curve E. The mean potential of the grid of tube ii is maintained at cut-oilE by a. battery or other voltage source H5; with the result that the iiuctuating grid-potential represented by the curve I causes plate current as represented by the the curve J to flow in the tube lill. noted that the curve J is identical with the curve F except that curve F leads curve J by one-fourth their common period.

The respective plate currents in the triodes |83 and ici are employed jointly with the control signal to regulate the operation of tetrodes |2 and 2i in each of which the two grids function as control grids. The cathode of tube |25) is grounded, while its plate is connected through an elcctromagnet 4| to the B+ source. The tube iii is reversely connected, its plate being grounded and its cathode being connected through an electromagnet '52' to a source of negative potential equal in absolute value to the B-lsource. One grid of the tube |253 is connected to the cathode of tube lili', one grid of tube il is connected to the cathode of tube lili, and the other grids of the two tubes are connected through condensers |22 to a conductor E23 over which the control signal We is transmitted. The plate of tetrode i 29 and the cathode of tetrode i2! are connected through condenser-s 69 with the low-potential terminal of the resistance 58.

The mechanical means employed in association with the electrical system of Fig. l0 to eiect automatic adjustment of the potentiometer 65 and movement of a controlled member may be one such as is illustrated in Fig. a. As will be evident from that ligure, the device is essentially It Will 'be i 14` the same as that shown in Figs. 7 and 8 except for the addition of an electromagnet 32 arranged to oppose the eifect of the electromagnet i2 on the brake mechanism 8c.

In Fig. 12, the curve F', which corresponds to the curve F of Fig. l1, represents variations in the potential or the screen grid in the tetrode |20; the curve J', which corresponds to the curve J of Fig. 11, represents variations in the potential of the screen grid of the tetrode |24; and the curve We indicates the control signal, which is impressed upon the control grids of both the tetrodes i223 and 12|. Fig. 12 illustrates a stablestate condition in which the variable voltages F and J both have the same frequency as the control signal We, the two grids of each of the tetrodes |26 and 12| are never above cut-oir potential at the same time, no plate current hows in either tetrode, and the magnets t i and 42 are ele-energized. In this condition, the electromagnets 82 and 8E of Fig. 16a operate to hold both brake mechanisms and -lii engaged, and the disk Si therefore remains stationary as do also the controlled member it (Fig. S) and the adjustable element of the potentiometer 65. This stable-state condition exists as long as no change occurs in the frequency or" Vile.

In the stable-state condition shown in the Voltage J leads the signal WC, whic in turn leads the voltage A decrease in the frequency of We will cause a progressive wave-to wave decrease in its phase displacement relative to the voltage with the result that there cour intervals of increasing duration in which both grids of the tetrode |29 are above cut-oil" potential. As a result, plate current flows through the tetrode l2@ and through the electromagnet 4|. The tetrode i is not immediately affected by a decrease in the frequency of the signal We because, as is clear from Fig'. 12, such a change would effect a progressive increase in the phase-displacement of We relative to J and would not result in the occurrence of intervals in which both grids or the tube |2i are simultaneously above their cut-oil potentials. Accordingly, although a decrease in the frequency of the signal We will energize the electromagnet 4|' (Fig. 10a) it will not energize the electromagnet 42. Energization of the magnet 4i releases the brake 'is while the brake remains engaged, the disk El is permitted to rotate to carry the frame '58 with it, and the controlled member 4c and the potentiometer cli are moved to decrease the frequency of the oscillator 25 and with it the frequency oi the voltages F and J. Eventually, a new stable-state condition is attained in which the controlled member occupies a new position.

Upon an increase in the frequency of the signal We following the existence of a stablestate condition, the resultant wave-to-wave change in phase displacement of the voltages We and J creates intervals of progressively increasing duration in which the grids of the tetrode |2| are both above cut-oil potential, with the result that plate current flows through the tetrode |2| and the electromagnet 42. An increase in the frequency of the control signal We has no immediate effect on the tetrode |2S, as it effects a progressive increase of the phase displacement of the signal We relative to the voltage F. Accordingly, the electromagnet 12 is ener gized to release the brake Si?, the electromagnet lli remains ele-energized to retain the brake i9 in engagement, and the adjustable element of the Fig. 12,

l5' potentiometer $5 mores with the controlled' member to increase the frequency of the oscillator 25 and eventually to cause the existence of a new stable-state condition at the higher frequency.

In the system of Fig. 1G, each of the condensers 69 functions with the resistance t3 in the saine way as does the condenser es in the system of Fig. 6, to accommodate for lag in the operation of the mechanical system and to expedite the attainment of a new stable-state condition following a change in frequency of the control signal. In addition, these condensers prevent the flow of direct current through the magnets lll and 42 from the source of positive B voltage to the source of negative B voltage.

The receiving circuit shown in Fig. 9a is similar to that of llig. l except for the location cf the milliammeter Eil and 22 which, in this instance, are connected in series with each other across a condenser 25 interposed between ground and the cathode of the tetro/.le 22. The control signal We and the local signal W5 are impressed respectively on the grids 22a .and 2217 of the tetrode 22, and hence jointly control plate current as in the system of Fig. l. Because of the impedance l25, the potential of the cathode of the tetrode 22 will vary with variations in plate current and may be employed to control the frequency of the local oscillator 25. Specifically, an increase in plate current, caused by a relative shift of the signals We and Ws toward an irl-phase relationship, will increase the potential of the cathode.

If the oscillator 2% in the system of `Fig. 9c responds to variations in control voltage as do the corresponoing oscillators of the other systems described-i. e., if its frequency varies in the same sense as the control voltage t the local signal Ws will lead the control signal We in any stable-state condition. lf the frequency of the control signal increases, the successive waves of the two signals will progressively shift toward the in-phase relationship to increase plate current and hence increase the potential of the cathode of tetrode 22; and as such cathode-p0- tential controls the frequency of oscillator 25, the frequency of the local signal will increase until it matches that of the control signal, and establishes a new stable-state condition characterized by a new phase relationship of the two signals, a new plate current, and a new reading of the milliammeter 2t. ln the other systems illustrated, in which an increase in plate current causes a decrease in the potential controlling the fre uency of the local signal, the control signal leads the local signal in any stable-state condition. In any of the systems, if the local oscillator were arranged so that its frequency varied in a sense opposite to that of the control voltage, the stable-state phase relationship of the two signals would be reversed.

The receiving systems described above, although employing the saine fundamental principle, operate in two different ways. ln the systems of Figs. l and 9, the frequency of the local signal Ws is controlled by the average current in the plate circuit of the tubeV 22, and for every different frequency of the control signal there is therefore a different average, stable-state plate current. ln the systems of Figs. o and l0, however, where the frequency of the local signal is controlled by an adjustable potentiometer, the average, stable-state plate current is the same for all frequencies. ln the former type of system, the frequencies respectively determined by the minimum and maximum attainable plate currents mark the limits of the band over which the frequency of the control signal can be varied. In the other type, if the rate at which the frequency of the control signal can be Varied is adequately limited, the range of variation is limited only by the range of adjustment of the device which controls the frequency of the local signal. However, if the rate at which the frequency of the control signal can be varied is unlimited, then the width of the band over which such frequency can be varied is limited by the necessity of preventing the occurrence of a condition such as is illustrated in Fig. 13.

lt is to be noted that the response of the receiving apparatus to a signal transmitted to it is substantially unaffected by variations in amplitude or harmonic distortions of such signal. This is so because the actual control signal is not the transmitted signal itself, but is instead a signal of equal frequency generated by a local oscillator whose output is of substantially constant amplitude. Generation of the actual control signal by an oscillator located at the receiving station but controlled in frequency by the transmitted signal, makes it possible to employ a control signal which has a different wave form from that of the transmitted signal. As brought out above, control signals of asymmetric square wave form have advantages in certain situations; but, in general, a transmitted signal of sine wave form is preferred to others because any other form requires a band width sufficient to admit at least one harmonic of the fundamental frequency of the transmitted signal.

The explanations of operation set forth abovev contain an assumption that the oscillators respectively generating the local and control signals are without any effect on each other. Actually, such is not the case. Referring to Fig. 6, for example, the presence of the condenser @t and the use of a common B-lsource for the oscillators i5 and d tend to result in synchronization of these oscillators. Such a tendency can be increased, decreased, substantially eliminated, or even shifted in phase, when desired, as by introducing a slight signal from the plate of tube 53 to the control grid of tube 53 or el t.rough an appropriate resistance-capacity network. Some inherent tendency of the oscillators 25 and t to synchronize is desirable, for it stabilizes operation of the mechanical system. However, the greater the tendency toward synchronisation the greater will be the change in the frequency of the transmitted signal required to produce a response at the receiving station.

have referred to my invention above as utilizing signals whose frequency is of the order of that of audio-frequency signals. It is not to be understood from. this, however, that the frequencies which can be employed are limited to those of audible sounds.

claim as my invention:

l. In a remote control system, a rotatable disk, means biasing said disk for rotation in one direction, a controlled member reciprocable along a' path arranged generally radially with respect to the axis of disk rotation, a pair of members mounted for movement circumferentialy of said disk and on opposite sides of said radial path, links connecting said last-named members to said controlled member, brake means releasably connecting each of said pair of members with said disk and biased toward engaged condition, electromagnetic means for selectively releasing said 17 brake means, and means responsive to movement of said controlled member for controlling said electromagnetic means to cause engagement of said brake means.

In a frequency-responsive receiver for use in a remote-control system, a variable-frequency oscillator, an electron discharge device having a cathode, a pair of control grids and an anode, an anode circuit for said device, said cathode, anode and grids being so arranged and said control grids so biased that the potential of each grid can limit current in the anode circuit to a minimum irrespective of the potential on the other grid whereby current Wiil flow in the anode circuit only during intervals when both grids are above their respective cut-oir potentials, means for impressing an incoming signal on one of said control grids, means for impressing on the other control grid the signal produced by said oscillator, and means responsive to the current flowing in said anode circuit for controlling the frequency of said oscillator.

18 3. The invention set forth in claim 2 with the addition of a movable member, and means responsive to the current in said anode circuit for moving said member.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 1,897,204 Loewe Feb. 14, 1938 2,176,742 La Pierre Oct. 17, 1939 2,280,019 Alexandersson et al. Apr. 14, 1942 2,342,816 Peek Feb. 29, 1944 2,395,575 Mitchell Feb. 25, 1946 2,396,091 De Bey Mar. 5, 1946 2,398,419 Finison Apr. 16, 1946 2,410,523 Rankin Nov, 5, 1946 2,429,771 Roberts Oct. 23, 1947 2,466,583 Dillman Apr. 5, 1949y 2,487,678 Stickel Nov. 8, 1949 2,557,581 Triman June 19, 1951 

